Yeah Mammon's really on the lower end of the Perfect Level Spectrum.
Parrotmon possibly? Feat wise they're certainly comparable enough that flight would probably be the determining factor in the 1v1, so 1v20 with all those ranged Tusk Strikes coming at once wouldn't be fun. Especially if Parrotmon gets hit with Tundra Breath at any point, being rendered immobile due to freezing.
On the same grounds, basically any Perfect Level that can be affected by an attack from an attack from an Adventure Adult (unless said Adult is Angemon), or that hasn't shown the capacity to one-shot other Perfect level Digimon (nor scales to one who has).
They could beat a few Perfect levels, just not all of them, probably stop somewhere in mid-tier.